Currently, work is in progress to set new standards, on which a long term evolution of the UMTS (Universal Mobile Telecommunication System) terrestrial radio access network (UTRAN) will be based. An evolved UTRAN (EUTRAN), also referred to as a 3.9G system in allusion to the current third-generation (3G) system, is expected to provide enhanced transmission performance. It is presumed that the 3.9G system will be based on the multi carrier technology of orthogonal frequency division multiple access (OFDMA) in the downlink (DL) radio transmission from the network to the subscribed wireless terminal devices. The uplink (UL) radio transmission technology of the coming 3.9G system is expected to be a single-carrier frequency division multiple access (SC-FDMA) technology.
In FDMA technology, an available frequency band is divided into sub-bands forming individual transmission channels. In SC-FDMA, a single sub-band is assigned to an uplink radio connection from a wireless terminal device to a wireless access network node.
An assumption regarding the frequency re-use for OFDM has been that the same 5 MHz carrier can be re-used in each cell, which is often referred to as full frequency re-use, or frequency re-use factor of 1. The main benefit of such a frequency re-use is mainly ease of deployment, given that no frequency planning is required. In the case of the introduction of OFDM in UTRAN, it would be also desirable to maintain this property, which is already available with WCDMA (Wideband Code Division Multiple Access). It is noted however that using the same 5 MHz carrier in each cell does not necessarily imply that all of the OFDM sub-carriers would be re-used equally in each cell.
Given a frequency re-use factor of 1, the system becomes interference-limited by the other cell interference, and the interference perceived by the receiver.
Coverage area probability is thus limited in orthogonal systems like OFDMA or SC-FDMA due to the other cell interference. The amount of other cell interference depends mainly on the frequency reuse of the system. From this point of view, 3.9G system is rather challenging since the working assumption is reuse 1 and at the same time good system performance with coverage area probability of 95% is targeted.
Other cell interference translates into degradation of the radio performance, i.e., Signal-to-Interference-Noise ratio (SINR) is degraded. The quality of service (QoS) of the radio link can be maintained by increasing the amount of processing gain (i.e., more coding or spreading). There are also other techniques like Interference Cancellation (IC) and Interference Rejection Combining (IRC) which can mitigate the other cell interference quite effectively.
GSM/EDGE (Global System for Mobile communications/Enhanced Data rates for GSM Evolution) systems utilize fixed frequency reuse combined with frequency hopping, while WCDMA systems mitigate other cell interference using spreading and channel coding.